Analog controlled mixer

Abstract

A system and method for merging two or more analog video signals under control of a third analog video signal. A standard video output from one processor's video signal digital to analog converter (DAC) is used as the control signal for the merging of two or more other video signals. This enables the video outputs of even highly diverse processing schemes to be easily merged. In its preferred embodiment, the system includes analog switching circuitry which is used to mix the video outputs from two or more different systems. The system also includes circuitry which converts the standard video output from a third processor into a large swing TTL signal which is used to control the analog switch.

What is claimed is: 
     
       1. A video signal mixer, comprising: (a) first and second generator means for providing first and second analog video signals containing first and second video data, respectively;   (b) third generator means for providing a third analog video signal containing third video data which can vary, at video data rate, independently of said first and second video data; and   (c) analog switch means having: (i) first and second inputs for receiving said first and second analog video signals, respectively;   (ii) a third switch select input for receiving said third analog video signal; and   (iii) an output providing an output signal, said output signal being selected from said first and second analog video signals in dependence upon said third analog video signal.     
     
     
       2. A mixer as claimed in claim 1, wherein said third analog video signal is supplied to said analog switch means via an input comparator. 
     
     
       3. A mixer as claimed in claim 2, wherein the input comparator comprises: an ECL comparator having: a first input receiving a reference DC voltage;   a second input receiving said third analog video signal; and   an ECL output;     an ECL/TTL converter for receiving said ECL output from said ECL converter, and for providing a TTL output;   a TTL buffer for receiving said TTL output from said ECL/TTL converter, and for providing a TTL-differential signal to said switch select input of said analog switch means; and   first and second cables adapted to supply said first and second analog signals from said first and second generator means to said analog switch means, each of said first and second cables having a first length, said third analog video signal being supplied from said third generator means to said comparator by a third cable of a second length, said first length being longer than said second length by an amount effective to delay said first and second analog video signals by an amount equal to a delay introduced into said third analog video signal by said input comparator.   
     
     
       4. A mixer as claimed in claim 2, wherein said input comparator and said analog switch means are operated by different supply voltages. 
     
     
       5. A mixer as claimed in claim 1, wherein said first and second analog video signals are supplied to said analog switch means via first and second unity gain buffers, respectively. 
     
     
       6. A mixer as claimed in claim 1, wherein said first to third generator means comprise: first to third video processor means, respectively, for providing digital signals; and   first to third digital-to-analog converters which provide said first to third analog video signals from said digital signals, respectively.   
     
     
       7. A mixer as claimed in claim 1, wherein said first to third generator means are synchronized by a common pixel clock. 
     
     
       8. A mixer as claimed in claim 1, wherein said first to third video signals are of the same video signal standard. 
     
     
       9. A mixer as claimed in claim 8, wherein said video signal standard is one of RS-343A or RS-170. 
     
     
       10. A mixer as claimed in claim 1, wherein: said first and second analog video signals each comprise first, second and third component signals; and   said analog switch means comprises first, second and third analog switches, wherein: said first analog switch receives said first component signals of said first and second analog video signals;   said second analog switch receives said second component signals of said first and second analog video signals;   said third analog switch receives said third component signals of said first and second analog video signals; and   said first to third analog switches have switch select inputs commonly receiving said third analog video signal.     
     
     
       11. A method for merging two or more analog video signals carrying pixel data, under control of a third analog video signal, comprising the steps of: (1) providing first and second analog video signals containing first and second video data, respectively;   (2) providing a third analog video signal containing third video data which can vary, at video data rate, independently of said first and second video data; and   (3) generating an output signal selected from said first and second analog video signals in dependence upon said third analog video signal.   
     
     
       12. The method of claim 11, wherein the third step further comprises the step of providing said third analog video signal to an analog switch means via an input comparator. 
     
     
       13. The method of claim 12, wherein the step of providing said third analog video signal to said analog switch means via an input comparator further comprises the steps of: nominalizing said third analog video signal via an ECL comparator having a reference DC voltage as a first input and said third analog video signal as a second input;   converting an ECL output of said comparator to a TTL compatible signal via an ECL/TTL converter; and   buffering said TTL signal for providing a TTL-differential signal to said switch select input of said analog switch means.   
     
     
       14. The method of claim 13, further comprising the steps of: generating said first and second analog signals in first and second signal generators, respectively, and propagating said first and second analog signals through first and second cables, respectively to said analog switch means; and   propagating said third analog signal through a third cable of a length shorter than the length of said first and second cables by an amount effective to cause a propagation delay of said first and second analog video signals substantially equal to a delay introduced into said third analog video signal by said input comparator.   
     
     
       15. The method of claim 12, further comprising the step of operating said input comparator and said analog switch means by different supply voltages. 
     
     
       16. The method of claim 12, further comprising the step of supplying said first and second analog video signals to said analog switch means via first and second unity gain buffers, respectively. 
     
     
       17. The method of claim 14, further comprising the step of providing digital signals for first to third digital-to-analog converters to provide said first to third analog video signals from said digital signals, respectively, wherein said first to third digital-to-analog converters comprise first to third video processor means within said first to third generator means. 
     
     
       18. The method of claim 17, further comprising the step of synchronizing said first to third generator means by a common pixel clock. 
     
     
       19. The method of claim 11, further comprising the step of providing said first to third video signals at the same video signal standard. 
     
     
       20. The method of claim 19, further comprising the step of providing said first to third video signals at the same video signal standard of RS-343A or RS-170.